This application claims the benefit of Japanese Application No. 2000-170019, filed on Jun. 7, 2001, which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a vehicle air conditioning system that integrally controls an air conditioner and an engine.
2. Description of the Related Art
A vehicle is equipped with an air conditioning system that controls temperature, humidity, air flow, and ventilation in a vehicle compartment. An air conditioner unit of this air conditioning system is comprised of a ventilator (having a ventilating function), a heater (having a heating function), and a cooler (having cooling and dehumidifying functions). The cooler executes the cooling and dehumidifying functions by heat exchange by evaporation and liquefaction of a refrigerant. The cooler is comprised of a compressor, a condenser, and a cooling unit (having an expansion valve and an evaporator). More specifically, refrigerant, in the form of a low pressure gas, is compressed by a compressor 12 and therefore changes it into a high temperature/high pressure gas. The gas refrigerant is then cooled and liquefied by wind due to traveling of the vehicle and a cooling fan, and the refrigerant, in the form of high pressure liquid, is rapidly expanded by the expansion valve 15 and becomes easier to atomize. Fins formed around the evaporator 16 deprive heat from the liquid refrigerant and change it into gas refrigerant. During the evaporation, the refrigerant is deprived of a large amount of heat, and changes into the low-pressure gas again and is returned to the compressor.
In the case of an engine that operates such an air conditioning system, if an air conditioner control switch is turned on while the engine is idling, a load for operating the compressor is applied to the engine. Accordingly, a throttle angle is increased to raise an idle speed.
Recently, a lean burn internal combustion engine, which is operated at a substantially leaner air-fuel ratio than a stoichiometrical air-fuel ratio in order to improve the fuel economy, has been developed. This lean burn internal combustion engine is operated at a lean air-fuel ratio in a light load operating range, e.g. when the engine is idling. If the air conditioner control switch is turned on while the lean burn internal combustion engine is idling, however, the engine requires a compressor operating torque. Accordingly, the idle speed is raised and the engine is inhibited from operating at the lean air-fuel ratio, so that the engine can be mandatorily operated at a stoichiometrical air-fuel ratio. This causes deterioration of the fuel economy. Further, the air conditioner load (i.e., the compressor torque) varies according to the season (the outside air temperature). The idle speed is ordinarily raised on the basis of the maximum air conditioner load in order to prevent the engine from stalling when the air conditioner operating load is increased. In this case, the compressor torque changes greatly and causes rough idling. Therefore, the idle speed overshoots and deteriorates the drivability.
To address this problem, a device as disclosed in Japanese Patent Provisional Publication No. 11-153052 has been developed. This publication discloses that, in a xe2x80x9ccontrol device for controlling an air-fuel ratio when an internal combustion engine is idling,xe2x80x9d if the air conditioner load is applied when the engine that is allowed to operate at a lean air-fuel ratio is idling, a refrigerant pressure at the outlet side of a compressor is detected as a value corresponding to the air conditioner load to control the air-fuel ratio.
In the above-mentioned conventional device disclosed in the Japanese publication, a refrigerant pressure sensor detects the refrigerant pressure at the outlet side of the compressor as a value corresponding to the air conditioner load, and a control unit controls the air-fuel ratio according to the detected refrigerant pressure.
The refrigerant pressure at the outlet side of the compressor, however, is nearly zero just after the air compressor starts operating, and the refrigerant pressure start rising when a predetermined period of time has elapsed after the compressor starts operating. That is, just after the compressor starts operating, the refrigerant pressure sensor detects the refrigerant pressure with delay. Thus, the refrigerant pressure cannot correspond to the actual air conditioner operating load. It is therefore impossible to control the air-fuel ratio according to the actual air conditioner load.
It is therefore an object of the present invention to provide a vehicle air conditioning system that controls an engine and an air conditioner according to an air conditioner operating load to thereby improve fuel economy and drivability.
To attain the above object, the present invention provides a vehicle air conditioning system comprising: a compressor driven by an engine and circulates a refrigerant for an air conditioner; an outside air temperature sensing device that senses an outside air temperature; a vehicle speed sensing device that senses a vehicle running speed; a compressor torque estimating device that estimates a compressor torque required by the compressor of the air conditioner, the compressor torque estimating device estimating a first compressor torque according to the outside air temperature sensed by the outside air temperature sensing device and the vehicle running speed sensed by the vehicle speed sensing device; and a control device for controlling an operational status of the engine according to the first compressor torque.